One type of camera-lens-mounted optical filter is a “cross filter” that produces bright lines in a cross shape at light sources such as illumination points.
Recently, among compact digital cameras not mountable with optical filters, there are also digital camera products that are capable of adding, as a special effect, a cross filter effect. Such cross filter effects are generally executed by image processing.
As methods of image processing to execute a cross filter effect, generally bright line synthesis is performed to high brightness regions of an image, with the following two possible types. A first method is to scan an image and search for high brightness regions, then to synthesize a pre-prepared bright line pattern one at a time onto the high brightness regions that have been found. Another method is to apply blur processing in one direction to an image of high brightness regions extracted from a source image, so as to produce thin, bright line extensions. In such a method, plural bright lines produced by applying blur processing in plural different directions (for example in two directions when producing a cross-shaped cross filter effect) are synthesized onto the source image.
When the bright lines are produced for all the high brightness regions extracted from the source image and synthesized onto the source image, bright lines are added to large surface area high brightness regions, resulting in an unsightly image with a dirty, stained impression. Moreover, when there are plural high brightness regions present at high concentrations, excessive bright lines are added which again results in an unsightly dirty impression.
There is however a method proposed, for example, to select, out of high brightness pixel groups selected from target image data, high brightness pixel groups that form high brightness pixel groups whose size is a specified brightness point permissible pixel size or smaller.
There is also a method proposed in which, when high brightness pixels selected from an image configure plural adjacent groups, a representative pixel is selected from out of the group as a processing target light source, and then a ray pattern is synthesized centered on the processing target light source.
There is also a method proposed in which, within each segment range of segmented image data, a pixel at a position where a presence density of first reference pixels whose brightness values are a first threshold value or higher are present at maximum density is determined as a second reference pixel, and light-streak image data is added to the image data so that the second reference pixel is substantially centered.
There is also a proposal in which a priority is determined based on specified conditions for high brightness regions identified in the input image, and when there are a specified number of the identified high brightness regions or greater, the specified number of high brightness regions are selected in sequence from the highest priority high brightness region, and then an enhanced image with the high brightness regions depicted enhanced is synthesized onto the input image.